爆轰驱动固体套筒压缩磁场计算及准等熵过程分析

采用构形磁流体力学计算程序SSS/MHD对炸药爆轰驱动固体套筒压缩磁场实验进行了一维磁流体力学模拟计算, 得到空腔磁场以及样品管内壁速度随时间的变化历程, 分别与磁探针和激光干涉测量的实验结果符合. 由分幅照相结果阐述了套筒压缩空腔磁场过程中的屈曲失稳和Bell-Plesset不稳定性现象. 分析了样品管和套筒中的磁扩散、涡流和磁压力的变化规律. 结果表明, 由于聚心运动下样品管和套筒的运动速度不同、电磁力和内爆作用力平衡等原因, 样品管内靠近磁腔处的磁场、涡流和磁压力均高于套筒内距磁腔相同位置处的结果. 讨论了样品管内距磁腔0.05 mm处的熵增随该点压缩度的变化, 最大熵增与样品管材料定容比热的比值在10%左右, 爆炸磁压缩实验过程的等熵程度较高.     

Influence of the effect of librations on energy exchange between ultrashort light counterpulses in a medium with Kerr nonlinearity

The influence of the effect of molecular librations on the interaction of high-power ultrashort counterpulses in Kerr liquids with anisotropic molecules is investigated. Molecular librations are shown to substantially affect the shape of the output pulses. A narrow peak with an intensity fourfold to fivefold higher than the input-pulse intensity develops on the leading edge. This peak is followed by a series of narrow damped spikes, the duration of which correlates with the libration time. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 398–401, May–June, 2000.     

Effective quantum efficiency in the pulsed homodyne detection of a n-photon state

Homodyne detection can be used to perform measurements on various quantum states of the light, such as conditional single photon states produced by parametric fluorescence processes. In the pulsed regime, the time and frequency overlap between the single photon wave packet and the local oscillator field plays a crucial role. We show in this paper that this overlap can be characterized by an effective quantum efficiency, which is explicitly calculated in various situations of experimental interest. Received 27 July 2000 and Received in final form 29 November 2000     

Ordering of diagnostic information in encoded medical images. Accuracy progression

A concept of diagnostic accuracy progression for embedded coding of medical images was presented. Implementation of JPEG2000 encoder with a modified PCRD optimization algorithm was realized and initially verified as a tool for accurate medical image streaming. Mean square error as a distortion measure was replaced by other numerical measures to revise quality progression according to diagnostic importance of successively encoded image information. A faster increment of image diagnostic importance during reconstruction of initial packets of code stream was reached. Modified Jasper code was initially tested on a set of mammograms containing clusters of microcalcifications and malignant masses, and other radiograms. Teleradiologic applications were considered as the first area of interests.     

Practical segment intersection with finite precision output

The fundamental problem of finding all intersections among a set of line segments in the plane has numerous important applications. Reliable implementations need to cope with degenerate input and limited precision. Representing intersection points with fixed precision can introduce extraneous intersections. This paper presents simple solutions to these problems and shows that they impose only a very modest performance penalty. Test data came from a data compression problem involving a map database.     

Energetic efficiency of laser thermonuclear targets with ablator shells made of beryllium materials: A comparative analysis

The energetic characteristics of the compression and burning of targets with beryllium and beryllium deuteride shells are compared. The characteristics considered include the hydrodynamic efficiency, the efficiency of energy transmission to the thermonuclear fuel, and the gain factor found from numerical simulation using the ‘Diana’ one-dimensional mathematical code. The calculations are carried out for direct-drive cryogenic laser targets with the ablator shells made of beryllium or beryllium deuteride with parameters corresponding to the third harmonic of energy of the neodymium-laser radiation with a pulse energy of 1–3 MJ. It is proved that the gain of beryllium hydride targets can be brought to the level of beryllium targets due to variations in the geometrical parameters of BeD₂ targets. It is shown that the fission of BeD₂ or BeDT ablators in reactor-scale targets could significantly contribute to the final thermonuclear yield. __________ Translated from Preprint No. 20 of the P. N. Lebedev Physical Institute, Moscow (2001).     

色散缓变光纤中增益系数的取值对皮秒脉冲孤子效应压缩的影响

从描述皮秒光脉冲在色散缓变光纤(FSDD)中所满足的非线性Schro¨dinger方程(NLS)出发,数值模拟了高阶皮秒脉冲在增益系数取值不同的色散缓变光纤中的孤子效应压缩,研究分析了增益系数所产生的影响。计算结果表明,对于孤子阶数确定的光脉冲,增益系数有一最佳取值范围,对应于孤子效应压缩的参量———脉冲压缩比有最佳值。讨论了初始啁啾的影响。     

基于磁通压缩技术的爆炸磁频率发生器的参数选择

 爆炸磁频率发生器是一种结构简单、小型化的电磁脉冲产生和辐射装置。为了优化其性能，从数学模型入手进行研究，得出输出信号所满足的Bessel函数，分析了在不同电参数下输出信号的模式及电路中的能量分配。研究结果表明，当电感变化到初始值的1/e所需时间与初始载波频率的乘积较大时，发生器的输出信号为振荡模式，且二者乘积越大，载波频率越高，对其辐射越有利。     

Curvature dependent surface energy for a free standing monolayer graphene: Some closed form solutions of the non-linear theory

Continuum modeling of a free-standing graphene monolayer, viewed as a two dimensional 2-lattice, requires specifications of the components of the shift vector that act as an auxiliary variable. The field equations are then the equations ruling the shift vector, together with momentum and moment of momentum equations. We present an analysis of simple loading histories such as axial, biaxial tension/compression and simple shear for a range of problems of increasing difficulty. We start by laying down the equations of a simplified model which can still capture bending effects. Initially, we ignore out of plane deformations. For this case, we solve analytically the equations ruling the auxiliary variables in terms of the shift vector; these equations are algebraic when the loading is specified. As a next step, still working on the simplified model, out-of-plane deformations are taken into account and the equations complicate dramatically. We describe how wrinkling/buckling can be introduced into the model and apply the Cauchy–Kowalevski theorem to get existence and uniqueness in terms of the shift vector for some characteristic cases. Finally, for the treatment of the most general problem, we classify the equations of momentum and give conditions for the Cauchy–Kowalevski theorem to apply.     

Computation of differential operators in aggregated wavelet frame coordinates

Manuel Werner ^{Adaptive wavelet algorithms for solving operator equations havebeen shown to converge with the best possible rates in linearcomplexity. For the latter statement, all costs are taken intoaccount, i.e. also the cost of approximating entries from theinfinite stiffness matrix with respect to the wavelet basisusing suitable quadrature. A difficulty is the constructionof a suitable wavelet basis on the generally non-trivially shapeddomain on which the equation is posed. In view of this, recentlycorresponding algorithms have been proposed that require onlya wavelet frame instead of a basis. By employing an overlappingdecomposition of the domain, where each subdomain is the smoothparametric image of the unit cube, and by lifting a waveletbasis on this cube to each of the subdomains, the union of thesecollections defines such a frame. A potential bottleneck withinthis approach is the efficient approximation of entries correspondingto pairs of wavelets from different collections. Indeed, suchwavelets are piecewise smooth with respect to mutually non-nestedpartitions. In this paper, considering partial differentialoperators and spline wavelets on the subdomains, we proposean easy implementable quadrature scheme to approximate the requiredentries, which allows the fully discrete adaptive frame algorithmto converge with the optimal rate in linear complexity.}